Pye PF8 Circuit - UK Vintage Radio Repair and Restoration Discussion Forum

Jon_G4MDC · 25th Jun 2020, 10:56 am

I wonder if anyone can help with this?

The PF8 was constructed using plug in modules some of which were conventional contruction while others were potted in epoxy. Of course the epoxy ones are pretty much unrepairable.

As far as I can remember the PF8 schematic treated each module as a box with only the functional symbol for what it does, multiplier, PLL, AF Amp etc.
Has anyone seen any more detailed info please?

I want to experiment with the DC/DC converter. It used 2x 1.2V NiCads and a DC/DC to ~10V for the main supply - I have no idea why they chose to do that. The DC/DC Converter is one of the "fixable" modules so the circuit could be traced out if needs be.

I would like to see if it would be safe to run it from a single 3.7V Lithium Cell or if it could be modified to do so.

davidw · 26th Jun 2020, 9:19 am

I haven't got a circuit but referencing the late Chris Lorek's first book on pmr conversions he says "connect a suitable 2.4v supply but NEVER (his emphasis) exceed 2.7v otherwise you're likely to damage the set's circuitry" suggesting I think that some mods will need to be done to facilitate 3.7v

Jon_G4MDC · 26th Jun 2020, 9:26 am

Interesting info. Thanks.

AdrianH · 26th Jun 2020, 10:01 am

This page any use there is a pdf manual at the bottom.

https://sites.google.com/site/g3xbmqrp3/vuhf/pf8

Adrian

Jon_G4MDC · 26th Jun 2020, 3:51 pm

Brilliant Adrian - thank you. There is more in the manual than I recalled.
The inverter circuit is there so it is exactly what I wanted to know.

My own manual is deep down a pile in the shed - now I don't need to scan it.

Jon_G4MDC · 26th Jun 2020, 8:33 pm

Now it gets interesting.

I have robbed a scrap set and here we find the Inductor/Transformer is AL21447 - I will be dissecting that.

The main DC/DC switch transistor is X44H260. Er - wassat then?? Might be K44H260.

The plug in PCB has most of the rest of the works.

Jon_G4MDC · 26th Jun 2020, 9:56 pm

Here is the ferrite core..
Looks like a gapped core without an adjuster fitted.
I have yet to look up the spec but it should not be too difficult to find.

Jon_G4MDC · 27th Jun 2020, 1:33 pm

The transformer has been disassembled now. It revealed why the set was scrapped. A probable impact with the hard deck has caused the ferrite mass to crack the former - there were no supporting legs on the side clips. The secondary winding had a break in it.

Here is my dissection in the hope it might be of some use to others.

I'm thinking to increase the 6 Turn primary to more like 9 Turns to allow for 3.7V instead of 2.4V supply. The original primary winding was 4 parallel strands of wire or ~24 turns total. I will probably cut back to 3 parallel strands for 27 turns total.

I will rewind this core and try it in a lash up first.

27th Jun 2020, 1:55 pm

Why not build a buck converter to change the (rather nominal) 3.7V from the LiIon cell to a proper 2.4V. Nicads have a very flat discharge curve unlike LiIon.

Jon_G4MDC · 27th Jun 2020, 2:00 pm

It's a thought if this doesn't work I suppose. Not much space though!

25th Jun 2020, 10:56 am	#1
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Pye PF8 Circuit I wonder if anyone can help with this? The PF8 was constructed using plug in modules some of which were conventional contruction while others were potted in epoxy. Of course the epoxy ones are pretty much unrepairable. As far as I can remember the PF8 schematic treated each module as a box with only the functional symbol for what it does, multiplier, PLL, AF Amp etc. Has anyone seen any more detailed info please? I want to experiment with the DC/DC converter. It used 2x 1.2V NiCads and a DC/DC to ~10V for the main supply - I have no idea why they chose to do that. The DC/DC Converter is one of the "fixable" modules so the circuit could be traced out if needs be. I would like to see if it would be safe to run it from a single 3.7V Lithium Cell or if it could be modified to do so.

26th Jun 2020, 9:19 am	#2
davidw Heptode Join Date: Sep 2006 Location: Woodbridge, Suffolk, UK. Posts: 643	Re: Pye PF8 Circuit I haven't got a circuit but referencing the late Chris Lorek's first book on pmr conversions he says "connect a suitable 2.4v supply but NEVER (his emphasis) exceed 2.7v otherwise you're likely to damage the set's circuitry" suggesting I think that some mods will need to be done to facilitate 3.7v __________________ Dave G1AGK. My perception is my reality! Last edited by davidw; 26th Jun 2020 at 9:22 am. Reason: addition

26th Jun 2020, 9:26 am	#3
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Pye PF8 Circuit Interesting info. Thanks.

26th Jun 2020, 10:01 am	#4
AdrianH Octode Join Date: Mar 2020 Location: Blackburn with Darwen, Lancashire, UK. Posts: 1,572	Re: Pye PF8 Circuit This page any use there is a pdf manual at the bottom. https://sites.google.com/site/g3xbmqrp3/vuhf/pf8 Adrian __________________ Asking questions and learning, or trying to! Youtube EF91Valve

26th Jun 2020, 3:51 pm	#5
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Pye PF8 Circuit Brilliant Adrian - thank you. There is more in the manual than I recalled. The inverter circuit is there so it is exactly what I wanted to know. My own manual is deep down a pile in the shed - now I don't need to scan it.

26th Jun 2020, 8:33 pm	#6
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Pye PF8 Circuit Now it gets interesting. I have robbed a scrap set and here we find the Inductor/Transformer is AL21447 - I will be dissecting that. The main DC/DC switch transistor is X44H260. Er - wassat then?? Might be K44H260. The plug in PCB has most of the rest of the works. Attached Thumbnails

26th Jun 2020, 9:56 pm	#7
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Pye PF8 Circuit Here is the ferrite core.. Looks like a gapped core without an adjuster fitted. I have yet to look up the spec but it should not be too difficult to find. Attached Thumbnails

27th Jun 2020, 1:33 pm	#8
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Pye PF8 Circuit The transformer has been disassembled now. It revealed why the set was scrapped. A probable impact with the hard deck has caused the ferrite mass to crack the former - there were no supporting legs on the side clips. The secondary winding had a break in it. Here is my dissection in the hope it might be of some use to others. I'm thinking to increase the 6 Turn primary to more like 9 Turns to allow for 3.7V instead of 2.4V supply. The original primary winding was 4 parallel strands of wire or ~24 turns total. I will probably cut back to 3 parallel strands for 27 turns total. I will rewind this core and try it in a lash up first. Attached Thumbnails Last edited by Jon_G4MDC; 27th Jun 2020 at 1:41 pm.

27th Jun 2020, 1:55 pm	#9
Guest Guest Posts: n/a	Re: Pye PF8 Circuit Why not build a buck converter to change the (rather nominal) 3.7V from the LiIon cell to a proper 2.4V. Nicads have a very flat discharge curve unlike LiIon.

27th Jun 2020, 2:00 pm	#10
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Pye PF8 Circuit It's a thought if this doesn't work I suppose. Not much space though!